This is section 34 of the FBI HQ main file on "Operation SOLO" which consists of 125 sections. The entire file may be seen here: https://vault.fbi.gov/solo
SOLO was an anti-Soviet Union and anti-Communist China counter-intelligence operation which involved “two informants in top echelon of the Communist Party”. The two FBI moles were Morris Childs and Jack Childs (also known by their respective FBI symbols CG-5824-S* and NY-694-S*.
CG = Chicago (where Morris lived)
NY = New York City (where Jack lived)
S = Security informant
Asterisk (*) designated person who could never testify in court or otherwise be identified.
One FBI memo describes the origins of the SOLO operation as follows:
“Solo is code name for operation involving CG-5824-S as official liaison representative between Communist Party (CP), USA, and Soviet Union. Information developed in 1956 that Soviets and CPUSA both desired better means of communication. Survey of this over-all matter reflected that CG-5824-S offered our best potential of penetrating any courier apparatus which might be set up between CPUSA and Moscow. Through careful guidance afforded by Chicago office and deft maneuvering on part of informant himself, CG 5824-S was ultimately selected by Eugene Dennis, CPUSA leader, to go to Moscow as official representative of CPUSA. This information was relayed to Soviets through Tim Buck, Canadian CP leader, and approval of CG-5824-S to act in this capacity was subsequently received by Moscow…Invaluable assistance in over-all operation was afforded by NY-694-S, brother of CG 5824-S. NY-694-S has long been engaged in courier operations between CPUSA and Canadian CP. He was recipient of original information that liaison might be established between Soviets and CPUSA…All problems and obstacles were ultimately surmounted and CG-5824-S (and one name redacted) departed for Moscow 4-24-58. They spent one month in Moscow, another month touring Russia and 12 days in China. During this period CG-5824-S conferred with most of highest ranking officials in Russia and China. He returned to this country on July 21, 1958.” [FBI HQ file 67-268746, serial #194; 8/28/58 memo regarding SOLO from F. J. Baumgardner to A.H. Belmont.]